When does sp_executesql refresh the query plan?
The line from MSDN is talking about using EXEC(), like this:
SET @sql = 'SELECT foo FROM dbo.bar WHERE x = ''' + @x + ''';';
EXEC(@sql);
In my testing, modern versions of SQL Server are still able to reuse a plan like this, but there may be other variables (such as version, or for example if you add conditional WHERE clauses based on the presence of certain parameters - in which case that will generate a different plan).
If you use sp_executesql then the parameter values can still cause parameter sniffing issues (just like with normal SQL), but this has nothing to do with whether SQL Server can re-use the plan. This plan will get used over and over again, just as if you hadn't used sp_executesql at all, unless variables that would cause a direct query to get recompiled, in which case this one will get recompiled too (essentially, SQL Server doesn't store anything with the plan that says "this was executed from sp_executesql, but this one wasn't):
SET @sql = N'SELECT foo FROM dbo.bar WHERE x = @x;';
EXEC sys.sp_executesql @sql, N'@x varchar(32)', @x;
As a bonus, this has built-in protection against dynamic SQL, and avoids you having to worry about doubling up single quotes due to string delimiters. I blogged about some of this here and please read up on SQL injection here and here.
If you are having issues with plan re-use and/or parameter sniffing, some things you should look into are OPTION (RECOMPILE), OPTIMIZE FOR, optimize for ad hoc workloads and simple/forced parameterization. I addressed a few similar questions in response to a recent webcast here, it may be worth a skim:
- Follow-up on Summer Performance Palooza 2013
The gist is: don't be afraid to use sp_executesql, but only use it when you need it, and only spend energy over-optimizing it when you have an actual performance issue. The example above is a terrible one because there's no reason to use dynamic SQL here - I've written this answer assuming you have a legitimate use case.
The queries which are run via sp_executesql follow the same rules of execution plans as normal queries which aren't run through sp_executesql. If the query text changes then a new plan is created. If the text doesn't change because of the user of parameters then the plan is reused. When the stats are updated then plans expire and new plans are generated the next time the query is run.